U.S. Secretary of State Condoleezza Rice is endorsing an international investigation into the assassination of former Lebanese Prime Minister Rafik Hariri. She also says the U.S. Ambassador to Syria will remain in Washington indefinitely - after being recalled for consultations. Meanwhile, Syria and Iran now say they will form a united front in the face of mounting challenges and threats from other countries.

Former Lebanese Prime Minister Hariri and at least 16 others were killed in a car bombing in Beirut Monday. Testifying before US lawmakers Wednesday, Secretary of State Rice did not directly blame Syria for the attack.

"We have been very clear that we don't know the - who is responsible for the bombing, but that there needs to be an international investigation of that," she said. "But the Syrians, given their position in Lebanon, given their interference in Lebanese affairs, given the fact that their forces are there, given the terrorists that operate in southern Lebanon with Syrian forces in close proximity to them - does put on the Syrians a special responsibility for the kind of destabilization that happened there and that this sort of thing could happen."

On Tuesday, the State Department stressed US outrage over the assassination - announcing the recall of U.S. Ambassador to Syria, Margaret Scobey.

Mr. Hariri was well respected in Washington as an independent voice in Lebanon, despite Syrian influence in the country. In addition, Washington has accused Syria of being a haven for anti-Iraqi insurgents.

Another country in the region under pressure from the US is Iran. The US and its European allies have been pushing Tehran to abandon its pursuit of nuclear weapons. On Wednesday, Iran and Syria said they will form a united front - to face the challenges and threats they are receiving from other countries. The announcement came after Syrian Prime Minister Naji Otri and Iran's Vice President Mohammad Reza Aref held talks in Tehran Wednesday.